1. Field of Invention
This invention relates to a casing unit for a circuit assembly that can be used as a power distributor on a vehicle for distributing an electrical power to a plurality of electronic units from a common power source on a vehicle, and also relates to a method for producing the circuit assembly.
2. Description of Related Art
Heretofore, as means for distributing an electrical power to each electronic unit from a common power source on a vehicle, a junction box has been known which constitutes a power circuit section in which a plurality of bus bar boards are laminated and a fuse and a relay switch are incorporated on the boards.
Recently, in order to downsize a junction box for distributing an electrical power to each electronic unit and to realize a high speed switching control, a circuit assembly in which a switching device such as an FET (a field-effect transistor) or the like has been developed to be interposed between an input terminal and an output terminal. It will be preferable to cool down the hot switching device in the circuit assembly effectively. In view of this cooling action, a circuit assembly has been proposed in which a power circuit section is stuck through an insulation layer on a circuit arrangement area on a circuit arrangement surface of a heat radiation member made of an aluminum or the like having good heat conduction. See, for example, Japanese Patent Public Disclosure No. HEI 11-204700.
In the circuit assembly in which the power circuit section is adhered to the circuit arrangement surface of the heat radiation member, for example, it is necessary to protect the power circuit section by a casing body. In this case, the power circuit section is pressed on the circuit arrangement surface from the outside of the casing to ensure a sticking condition after mounting the casing body on the heat radiation member and an inspection of a circuit condition is carried out after mounting the casing body on the heat radiation member. It will be necessary to provide an opening having a certain size in the casing body to expose the power circuit section outwardly.
On the other hand, the casing body can be mass-produced by pouring a heated molten synthetic resin into a mold. However, if a large opening is provided in the casing body, the casing body might be deformed because of a shrinkage cavity caused upon cooling after forming. There is a possibility of encountering a difficult assembling in the worst case.
An object of the embodiments of the present invention is to provide a circuit assembly including a casing unit having a good configuration and a method for producing the circuit assembly.